Archived posting to the Leica Users Group, 2001/12/05

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Subject: Re: [Leica] SF-20: Wrong Setting but OK?
From: "Bob Parsons" <bobp@ntlworld.com>
Date: Wed, 5 Dec 2001 13:58:58 -0000
References: <a4.1d6435f1.293f4a29@aol.com>

Jo Goodtimes wrote:
> Hello Jerry . 
> I think I have an explanation but I'm not sure . 
> Since the diaphragm setting isn't coupled to the flash ,
> it only controls the areas exposed by natural light .
> If you were in TTL mode , the cell behind the lens of your 
> M6 actually controlled the flash power . 
> Now this drives to a question : is it necessary to adjust the 
> diaphragm on the flash in TTL mode ? 
> Maybe not .

As far as I understand, in TTL mode you don't need to tranfer
the lens aperture setting to the flash, in spite of saying on page
40 of the manual that you must. You only need to tell the flash
the lens aperture if you want to use the inbuilt max/min distance
calculator, see page 50 in the manual. With the R8 the aperture
is automatically communicated to the flash as soon as you apply
first pressure to the shutter release and the distance display
changes as you rotate the lens aperture ring.

I think the way fill in works in TTL and A modes, is that the flash
intensity is higher and shorter duration than the film illumination
from the natural light falling on the scene. The flash may be 1/10,000
sec and the total film exposure 1/50 sec. This means the natural
illumination has little effect on the flash metering circuits. The flash
fill/exposure is determined by the lens aperture actually set on the
lens, film speed (set by camera in TTL mode or manually on flash
in A mode), +/- exposure compensation set on flash and scene
reflectivity.

For fill in I need to find the limits of film speed and maximum lens
aperture when using an 85B filter (tungsten fill) over the flash with
and without the diffuser. I suspect using 800 ASA Portra and f 1.4
- -2.0 I'll need a neutral density filter over the flash when in non TTL
A mode.

Bob Parsons bobp@dodo.demon.co.uk 



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Replies: Reply from "Jerry S. Justianto" <jsjm6@cbn.net.id> (Re: [Leica] SF-20: Wrong Setting but OK?)
In reply to: Message from V8PWR@aol.com (Re: [Leica] SF-20: Wrong Setting but OK?)